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Full text of "Handbook Of Chemical Engineering - I"

MATERIAL HANDLING—TRANSPORTATION OF SOLIDS         93
Fixed charges, consisting of interest on investment, insurance and taxes, etc., amount to about 8H Per cent of the initial cost of equipment.
Labor expense, almost a negligible factor with belt conveyors, may be arbitrarily set at 1H cts. per inch of width of conveyor per hour, irrespective of the load handled. Incidental expenses for supplies to keep the equipment in good operating condition vary closely with the power requirements and may be taken at % ct. per horsepower per hour.
The total expense of operating a belt conveyor system is best expressed in cost per ton of material handled and this is best illustrated by a specific example.
Example.—Required the net operating cost per ton of a 400-ft. conveyor handling 60,000 tons of fine coal during 1,200 operating hours in the year. The conveyor to elevate the coal 24 ft. and distribute it by means of an automatic tripper over a bunker 60 ft. long. Power delivered at the conveyor drive commands a value of 3 cts. per horsepower.
Advisable speed of conveyor (Table 7) = 400 ft. per minute.
Minimum capacity of conveyor (60,000/1,200) = 50 tons per hour.
Minimum capacity of conveyor at 100 ft. per minute, 12.5 tons per hour.
Fine coal weighs 50 Ib. per cubic foot, so required size of conveyor (Table 8) equals 14 in.
Power requirements:
__                       (0.00009 X 142 X 400 + 0.08 X 50) 400 + 50 X 24 ^        .     ,0. Horsepower =----------------------------------TOOO--------------------------------Formula   (8)
5.62—say 6 hp.
Additional horsepower for tripper......4           (14 — 10)
Total.............................To
Costs:
RCbc = (0.45 X 14 - 1.7)400 + 3.65 X 14 = 1,291.10              Formula (9)
RCat = 11 X 14 + 132.5 + 0.81 X 60 = 335.10                      Formula (9c)
Total relative cost = 1,291.10 + 335.10 = 1,626.20.
Take market price at 25 per cent above relative costs.
Cost = 1.25 X 1,626.20 = 2,032.75—say $2,000.00
Fixed charges:              (0.085 X 2,000).....................  $170.00
Labor charge:               (0.015 X 14)1,200...................    252.00
Supply expense:           (0.0075 X 10)1,200..................      90.00
Power charge:              (0.03 X 10)1,200...................    360.00
Depreciation expense: 1.25 X RDbc
= 1.25(0.08 X 14 - 0.32)400 + 0.365 X 14 = 51.10    say      50.00
S922.00 Net operating cost:   (922/60,000)..................  $0.0154 per ton
Flight conveyors are endless chains (one or two) carrying attached flights and dragging the load through troughs. Flights may rest on the inclined sides of the trough, be suspended from supporting and wearing shoes (shoe flight conveyors) or may be supported by flanged rollers running on rails (roller flight conveyors).
Flights, unless supported on the inclined sides of the trough, are usually rectangular, with their length two and one-half to two times their width, and equally spaced from 12 to 24 in. Sheet-steel flights are customarily used, unless the service is so exacting as to require cast or malleable iron. Troughs are usually steel lined and clearance should be provided between the bottom edge of the flights and the trough bottom for the collection of a protecting covering of fines.